docs: def load_codebook(self, filename):
          """Load the codebook from a file to the Somoclu object.
  
          :param filename: The name of the file.
          :type filename: str.
          """
          self.codebook = np.loadtxt(filename, comments='%')
          if self.n_dim == 0:
              self.n_dim = self.codebook.shape[1]
          if self.codebook.shape != (self._n_rows * self._n_columns,
                                     self.n_dim):
              raise Exception("The dimensions of the codebook do not "
                              "match that of the map")
          self.codebook.shape = (self._n_rows, self._n_columns, self.n_dim)